Determination of a threshold compromise value for the perfusion index by laser Doppler imaging after digital revascularization.

We have used laser Doppler imaging to monitor the microcirculation of replanted digits during the post-operative period in 103 patients who underwent either replantation after traumatic amputation or toe-to-finger reconstruction. The blood flow (perfusion unit) in each revascularized digit was compared with that of an unaffected digit. The perfusion index was defined as the perfusion value of a revascularized digit divided by the perfusion value of the neighbouring normal digit. The ideal threshold value of the perfusion index (0.397) was calculated by determining the receiver operating characteristic curve with optimal sensitivity and specificity. The corresponding Youden's index was 0.828. We believe that by establishing a threshold, that laser Doppler imaging should provide a reliable and objective assessment for the development of perfusion compromise in revascularized digits. LEVEL OF EVIDENCE: III.